Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, and relates particularly to an apparatus that has a function for controlling a fuel injection amount in order to accelerate warm-up of a catalyst.
Description of the Related Art
Conventionally, immediately after cold start of an internal combustion engine, a fuel injection amount is controlled in order to rapidly raise the temperature of a catalyst used for exhaust emissions control until an activation temperature is reached. According to an apparatus disclosed in, for example, Japanese Patent Laid-Open No. 2008-095542, a wastegate valve located along a bypass passage used for bypassing a turbocharger is opened at the start of an internal combustion engine to raise the temperature of a catalyst, and when the catalyst temperature has reached a predetermined value at which the combustible components of exhaust gas can be burnt, the wastegate valve is closed, and at the same time, dither control for alternately repeating the increase and the decrease of the fuel injection amount is performed (A/F oscillation in the present invention). When as the result of the dither control, oxygen is supplied by lean combustion, and combustible components, such as CO (carbon monoxide), is supplied by rich combustion, the oxidation reaction of CO in the catalyst is enhanced, the catalyst is heated by heat generation due to the oxidation reaction, and warm-up of the catalyst is accelerated. Since the execution of the dither control is permitted only in a case where the catalyst temperature is a predetermined level or higher, and since the exhaust gas is stirred by a gas mixture flowing through the turbocharger during the dither control, slipping of unburned components, such as CO and HC, through the catalyst can be suppressed.
According to Japanese Patent Laid-Open No. 2007-332867, in a case where the amount of spark retard is at a predetermined value or lower, an apparatus that performs dither control adjusts the wastegate valve to an opening direction. When the wastegate valve is controlled to an opening direction, the flow rate of exhaust gas to the turbocharger is reduced, and therefore, the increase in the turbine rotational speed of the turbocharger is suppressed during the rich combustion, and the torque output variation can be suppressed.
However, according to the apparatus proposed in Japanese Patent Laid-Open No. 2008-095542, when the wastegate valve is closed and the dither control is started after the catalyst temperature has reached the predetermined level, immediately afterwards, a delay occurs in the activation of the catalyst because the heat of the exhaust gas is transferred to the turbocharger, and unburned components, such as CO and HC, are slipped out through the catalyst, so that emission is degraded. Further, for the apparatus proposed in Japanese Patent Laid-Open No. 2007-332867, there is no means provided to solve a problem caused by the heat being transferred to the turbocharger when the catalyst is to be activated by starting dither control.